tests/test-issue1089.t

dirstate: rename _parentwriters to _changing_level

We will have context for changing more than parents, so lets be prepared.

https://bz.mercurial-scm.org/1089

  $ hg init repo
  $ cd repo
  $ mkdir a
  $ echo a > a/b
  $ hg ci -Am m
  adding a/b

  $ hg rm a
  removing a/b
  $ hg ci -m m a

  $ mkdir a b
  $ echo a > a/b
  $ hg ci -Am m
  adding a/b

  $ hg rm a
  removing a/b
  $ cd b

Relative delete:

  $ hg ci -m m ../a

  $ cd ..